1. Field of the Invention
The present invention relates to a surface acoustic wave device, and an environmental difference detecting apparatus using the surface acoustic wave device.
2. Description of the Related Art
Conventionally, there is well known a surface acoustic wave device comprising: a substrate having a surface capable of exciting a surface acoustic wave (SAW) and propagating the excited surface acoustic wave: and an electro-acoustic transducing element capable of exciting the surface acoustic wave along a surface of the substrate, propagating the surface acoustic wave along the surface, and receiving the propagated surface acoustic wave.
A surface acoustic device is used as a delay line, an oscillating device, a resonating device, a frequency selecting device, a variety of sensors including, for example, a chemical sensor, a biological sensor and a pressure sensor, or a remote tag, etc.
International Publication WO 01/45255 discloses a spherically shaped surface acoustic wave device. A substrate of the spherically shaped surface acoustic device has a spherically shaped surface capable of exciting a surface acoustic wave and propagating the excited surface acoustic wave. An electro-acoustic transducing element of the spherically shaped surface acoustic wave device is arranged in a band shaped zone having a predetermined width and being continuous in an annular shape on the spherically shaped surface of the substrate. The electro-acoustic transducing element is configured to propagate the surface acoustic wave excited along the surface in a direction in which the band shaped zone is continuous, and to repeatedly circulate the propagated wave.
The spherically shaped surface acoustic wave device can repeatedly circulate the surface acoustic wave, which is excited by the electro-acoustic transducing element in the band shaped surface acoustic wave propagating zone of the substrate that is continuous in the annular shape, in the band shaped zone without substantially attenuating the surface acoustic wave.
In order to propagate a surface acoustic wave along a surface of a substrate of a surface acoustic wave device, the whole substrate is made of a material capable of being excited to generate a surface acoustic wave and capable of propagating the excited surface acoustic wave, or alternatively is made by adhering a thin film, which is formed of a material capable of being excited and propagating a surface acoustic wave, on its surface.
It is known that the substrate formed of a combination with the thin film is high in manufacturing cost and is unsuitable for a mass-production at the present stage. It is also known that, in the substrate formed of only the material capable of being excited and propagating the surface acoustic wave, a difference occurs in a performance of propagating the surface acoustic wave such that the surface acoustic wave cannot be propagated or circulated depending on a direction in which an attempt is made to propagate the surface acoustic wave. Along the surface, it is difficult to propagate or circulate the surface acoustic wave in a plurality of different directions from each other.
The present invention has been made under the above-described circumstances, and an object of the present invention is to provide a surface acoustic wave device suitable to a mass-production and capable of always stably achieving a good surface acoustic wave propagation performance, and an environmental difference detecting apparatus using the surface acoustic wave device.